Sunglasses are needed to protect you from harmful rays, particularly ultraviolet and blue light, and the greater risk to you is when the sun is on eyeline.
Blue light damages the macula over time and is of more concern on cloudless days or if you are near water. Levels of ultraviolet light can be difficult to assess as this is invisible, but will generally be greater on brighter days and those with low cloud or mist. Children’s eyes are less well protected than those of older people as they are more transparent and it is thought that a significant degree of the damage seen in later life is a result of much earlier exposure.
The depth of tint required will vary with the ambient conditions and photochromic materials are very useful for coping with a wide range of brightnesses. The new designs change more quickly and have a greater variation of transparency especially when provided with anti-reflection coatings. However they do not work as well behind glass such as windscreens, and will eventually darken less with time.
We have had some success with pre-tinted photochromics such as Serengeti Drivers which do not go as pale as normal spectacles but do enhance contrast and help with dappled light. These come in prescription wear also.
Oakley provide a wide range of tints for different conditions, and their prescription range is very popular. See http://www.oakley.com/innovation/optical-superiority/lens-tints for their range.
Also for skiing we have Bolle and Adidas masks and goggles for all ages and prices.
And for those of us who are fashion victims it is possible to look cool and be sensible with the following brands: